Aromatic tetradentate phosphine

ABSTRACT

An improved process for the production of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon comprises contacting the carbon monoxide and hydrocarbon under polymerization conditions in the presence of a reaction diluent and a novel catalyst composition formed from a palladium compound, a strong non-hydrohalogenic acid and a tetradentate aromatic phosphine ligand. The polymer products are of higher molecular weight and are produced at a faster rate than the more conventional process employing a catalyst composition formed from a bidentate ligand.

This is a division, of application Ser. No. 07/503,414, filed Mar. 30,1990 now U.S. Pat. No. 5,057,599.

FIELD OF THE INVENTION

This invention relates to the production of linear alternating polymersof carbon monoxide and at least one ethylenically unsaturatedhydrocarbon. More particularly, the invention relates to an improvedprocess for the production of such polymers and to novel catalystcompositions employed in the process.

BACKGROUND OF THE INVENTION

The class of polymers of carbon monoxide and olefin(s) has been knownfor some time. Brubaker, U.S. Pat. No. 2,495,286, produced such polymersof relatively low carbon monoxide content in the presence of freeradical initiators, e.g., peroxy compounds. G.B. 1,081,304 producedsimilar polymers of higher carbon monoxide content in the presence ofalkylphosphine complexes of palladium salts as catalyst. Nozaki extendedthe reaction to produce linear alternating polymers in the presence ofarylphosphine complexes of palladium moieties and certain inertsolvents. See, for example, U.S. Pat. No. 3,694,412.

More recently, the class of linear alternating polymers of carbonmonoxide and at least one ethylenically unsaturated hydrocarbon hasbecome of greater interest in part because of the greater availabilityof the polymers. The more recent processes for the production of suchpolymers, now known as polyketone polymers or polyketones, areillustrated by a number of published European Patent Applicationsincluding 121,965, 181,014, 213,671 and 257,663. The processes generallyinvolve a catalyst composition formed from a compound of palladium,cobalt or nickel, the anion of a strong non-hydrohalogenic acid and abidentate ligand of phosphorous, arsenic, antimony or nitrogen. Thescope of the polymerization is extensive but, without wishing to belimited, a preferred catalyst composition has typically been formed froma compound of palladium, the anion of a non-hydrohalogenic acid having apKa below about 6 and a bidentate ligand of phosphorus. The resultingpolyketone polymers are thermoplastic materials of a relatively highmolecular weight and are processed by methods conventional forthermoplastics into a variety of shaped articles of established utility.

In the production of the linear alternating polymers, both the rate ofpolymerization and the molecular weight of the polymer are importantfrom economic considerations. A higher rate of reaction will, of course,produce more polymer per unit time. For many applications of thepolyketone polymers the products of higher molecular weight are moreuseful. Unfortunately, the increased reaction temperatures whichfacilitate higher reaction rates generally result in polymer product oflower molecular weight. In practice, the reaction temperature is oftenselected to obtain polymer of the desired molecular weight and whateverreaction rate which results from that reaction temperature must beaccepted. It would be of advantage to provide a process for theproduction of linear alternating polymers of carbon monoxide and atleast one ethylenically unsaturated hydrocarbon which proceeds at anacceptable reaction rate but produces polymer product of an acceptablemolecular weight.

SUMMARY OF THE INVENTION

The present invention provides an improved process for the production oflinear alternating polymers of carbon monoxide and at least oneethylenically unsaturated hydrocarbon. More particularly, the inventionprovides a process for the production of such linear alternatingpolymers in the presence of certain novel catalyst compositions formedfrom, inter alia, a tetradentate ligand of phosphorus. The inventionalso relates to the novel catalyst compositions.

DESCRIPTION OF THE INVENTION

The polyketone polymers which are produced by the improved process ofthe invention are linear alternating polymers of carbon monoxide and atleast one ethylenically unsaturated hydrocarbon. Suitable ethylenicallyunsaturated hydrocarbons which are useful as precursors of the linearalternating polymers have up to 20 carbon atoms inclusive, preferably upto 10 carbon atoms inclusive, and are aliphatic such as ethylene andother α-olefins including propylene, 1-butene, isobutylene, 1-hexene,1-octene and 1-dodecene, or are arylaliphatic containing an arylsubstituent on an otherwise aliphatic molecule, particularly an arylsubstituent on a carbon atom of the ethylenic unsaturation. Illustrativeof this latter class of ethylenically unsaturated hydrocarbons arestyrene, p-methylstyrene, p-ethylstyrene and m-isopropylstyrene.Preferred polyketone polymers are copolymers of carbon monoxide andethylene or terpolymers of carbon monoxide, ethylene and a secondethylenically unsaturated hydrocarbon of at least 3 carbon atoms,particularly an α-olefin such as propylene.

The structure of the polyketone polymers is that of a linear alternatingpolymer and the polymer contains substantially one molecule of carbonmonoxide for each molecule of hydrocarbon. When the preferredterpolymers are produced according to the invention there will be atleast about 2 units incorporating a moiety of ethylene for each unitincorporating a moiety of the second hydrocarbon. Preferably, there willbe from about 10 units to about 100 units incorporating a moiety ofethylene for each unit incorporating a moiety of the second hydrocarbon.The polymer chain is therefore represented by the repeating formula##STR1## wherein G is the moiety of the second ethylenically unsaturatedhydrocarbon polymerized through the ethylenic unsaturation thereof andthe ratio of y:x is no more than about 0.5. When the preferredcopolymers are produced there will be no second hydrocarbon present andthe copolymers are represented by the above formula I wherein y is zero.When y is other than zero, i.e., terpolymers are produced, the --CO--CH₂CH₂ -- units and the --CO--G-- units will be found randomly throughoutthe polymer chain and the preferred ratios of y:x are from about 0.01 toabout 0.1. The end groups or "caps" of the polymer chain will dependupon what materials were present during the polymerization and how orwhether the polymer was purified. However, the precise nature of the endgroups does not appear to influence the properties of the polymer to anyconsiderable extent so that the polymer is fairly represented by theformula for the polymer chain as depicted above.

Of particular interest are the polymers of the above formula I of numberaverage molecular weight from about 1000 to about 200,000, particularlythose of molecular weight from about 20,000 to about 90,000, asdetermined by gel permeation chromatography. The physical properties ofthe polymer will depend in part on the molecular weight of the polymer,whether the polymer is a copolymer or a terpolymer and, in the case of aterpolymer, the nature of and the proportion of the second hydrocarbonpresent. Typical melting points for polyketone polymers producedaccording to the invention are from about 175° C. to about 300° C., moreoften from about 210° C. to about 270° C. The polymers will have alimiting viscosity number (LVN), measured in a standard capillaryviscosity measuring device in m-cresol at 60° C., of from about 0.5 dl/gto about 10, but the preferred polymers have limiting viscosity numbersfrom about 0.8 dl/g to about 4 dl/g.

The present polymerization process employs a catalyst composition formedfrom a palladium compound, a non-hydrohalogenic acid having a pKa lessthan about 6, preferably less than 2, and a tetradentate ligand ofphosphorus. The palladium compound is preferably a palladium alkanoateand palladium compounds such as palladium acetate, palladium propionate,palladium butyrate and palladium hexanoate are satisfactory.Particularly preferred as the palladium compound is palladium acetate.The preferred anion is the anion of a non-hydrohalogenic acid having apKa below 2 (as measured in water at 18° C.). Acids which are suitablesources of anion include oxygen-containing inorganic acids such assulfuric acid and perchloric acid and organic acids including carboxylicacids such as trichloroacetic acid, dichloroacetic acid andtrifluoroacetic acid as well as sulfonic acids such as p-toluenesulfonicacid, methanesulfonic acid and trifluoromethanesulfonic acid. The acidstrifluoroacetic acid and p-toluenesulfonic acid are particularlypreferred, especially trifluoroacetic acid. The anion is preferablyprovided to the catalyst composition as the free acid but alternativelythe anion is provided as a metal salt, particularly a non-nobletransition metal salt such as a copper salt or a nickel salt. In yetanother embodiment part or all of the anion is provided as the palladiumsalt, e.g., palladium trifluoroacetate. However provided, the anion issupplied in a quantity of from about 1 mol to about 1000 mols per mol ofpalladium. Preferred quantities of anion are from about 2 mols to about100 mols per mol of palladium.

The tetradentate ligand of phosphorus is a tetrakis(diarylphosphino)compound of up to 40 carbon atoms having 4 diarylphosphino groups assubstituents in an organic molecule in which at least two carbon atomsseparate phosphino groups. A variety of such tetrakis(diarylphosphino)compounds are known and are suitable. Illustrative of such compounds arethose of the types listed below together with an illustrative method ofsynthesis.

A. A 1,2,3,4-tetrakis(diphenylphosphino)-1,3-butadiene produced byreaction of 1,2-bis(diphenylphosphino)acetylene with diphenylphosphine,

B. N,N,N',N'-tetrakis(diphenylphosphinomethyl)ethylenediamine which maybe prepared by reacting ethylenediamine with formaldehyde anddiphenylphosphine,

C. N,N,N',N'-tetrakis(diphenylphosphinomethyl)hydrazine produced byreacting hydrazine with diphenylhydroxymethylphosphine,

D. tetrakis(diphenylphosphinomethyl)methane produced by halogenatingpentaerythritol and reacting the resulting tetrahalide with sodiumdiphenylphosphide,

E. the tetrakis compound obtained by brominating durene withN-bromosuccinimide and reaction of the resulting tetrabromo compoundwith sodium diphenylphosphide,

F. the tetrakis compound obtained by reacting2-hydroxy-1,3-(diphenylphosphino)propane with terephthaloyl dichloride,

G. the tetrakis compound obtained by reacting2-hydroxy-1,3-bis(diphenylphosphino)propane with4,4'-diisocyanatodiphenylmethane,

H. the tetrakis compound obtained by reacting2-hydroxy-1,3-bis(diphenylphosphino)propane with the diglycidyl ether of2,2-di(4-hydroxyphenyl)propane,

I. the tetrakis compound obtained by reacting2-hydroxy-1,3-bis(diphenylphosphino)propane with1,4-di(chloromethyl)benzene,

J. the tetrakis compound obtained by reacting1,4-di[(2-chloromethyl-3-chloro)propyl]benzene with an alkali metaldiarylphosphide.

The preferred tetrakis(diarylphosphino) compounds are those of theformula ##STR2## wherein R independently is aryl of up to 10 carbonatoms inclusive including hydrocarbyl aryl such a phenyl, tolyl, xylylor naphthyl, or substituted-hydrocarbyl containing substituents havingatoms other than carbon or hydrogen, particularly in the form of polarsubstituents at least one of which is located in a ring position orthoto the carbon atom through which the aryl group is connected to aphosphorus. The preferred polar substituents are alkoxy groups andillustrative substituted-hydrocarbyl aryl groups include2-methoxyphenyl, 2-ethoxyphenyl, 2,4-dimethoxyphenyl, 2,6-diethoxyphenyland 2,4,6-trimethoxyphenyl. The R groups phenyl and 2-methoxyphenyl areparticularly preferred. In the above formula II the term "n" is aninteger from 0 to about 14 inclusive but preferably is an integer from 0to about 10.

The tetrakis(diarylphosphino) compounds of formula II are novelcompounds although they are most easily produced by conventional methodssuch as by reacting the corresponding alcohol, a tetraol, with asulfonic acid chloride such as p-toluenesulfonic acid chloride toproduce the tetra sulfonic acid ester and subsequent reaction of thetetraester with an alkali metal diarylphosphide. Thetetrakis(diarylphosphino) compound is employed in a quantity from about0.25 mol to about 25 mols per mol of palladium but preferably in anamount from about 0.5 mol to about 10 mols per mol of palladium.

In order to enhance catalytic activity it is useful on occasion toadditionally provide to the catalyst composition solution an organicoxidant. Suitable oxidants include quinones, both 1,2-quinones and1,4-quinones, organic nitrites such as butyl nitrite and organic nitrocompounds such as nitrobenzene and 2,4-dinitrotoluene. The preferredorganic oxidants are the quinones, particularly 1,4-quinones such as1,4-benzoquinone, 1,4-naphthoquinone and 1,4-anthraquinone. Especiallypreferred is 1,4-benzoquinone. As previously stated the provision oforganic oxidant is not required and amounts of oxidant up to about10,000 mols per mol of palladium are satisfactory. When oxidant isemployed, amounts of oxidant from about 10 mols to about 5000 mols permol of palladium are preferred.

The polymerization process of the invention is conducted by contactingthe carbon monoxide and hydrocarbon reactants under polymerizationconditions in the liquid phase in the presence of a reaction diluent.Alkanols are suitably utilized as reaction diluents, e.g., methanol andethanol. Methanol is preferred. The contacting takes place in a suitablereactor and is more efficient if some means of agitation such as shakingor stirring is provided. The molar ratio of carbon monoxide to totalethylenically unsaturated hydrocarbon is from about 10:1 to about 1:10but preferably is from about 5:1 to about 1:5. Sufficient catalystcomposition is employed to provide from about 1×10⁻⁷ mol to about 1×10⁻³mol of palladium, preferably from about 1×10⁻⁶ mol to about 1×10⁻⁴ molof palladium, per mol of olefinically unsaturated hydrocarbon.

Typical polymerization conditions include a reaction temperature fromabout 25° C. to about 150° C., but reaction temperatures from about 30°C. to about 130° C. are more commonly utilized. The reaction pressure issuitably from about 2 bar to about 150 bar but is preferably from about5 bar to about 100 bar. At the conclusion of polymerization the reactionis terminated as by cooling the reactor and releasing the pressure. Thepolymer product is customarily obtained as a material substantiallyinsoluble in the reaction diluent and is recovered by conventionalprocedures such as filtration or decantation. The polymer is used asobtained or is purified as by contact with a solvent or extraction agentwhich is selective for catalyst residues.

The process of the invention provides the improvement of a fasterreaction rate and a higher molecular weight (as reflected in a higherLVN) for the polymer product as compared with related processesemploying a bidentate phosphine ligand. This improvement appears to beparticular to process wherein the catalyst composition is formed from,inter alia, a tetradentate phosphine ligand. A corresponding processemploying a catalyst composition formed from a tridentate does notprovide a similar improvement and in general is inferior to the processemploying a catalyst composition formed from a bidentate ligand. Thepolymer product finds utility as a premium thermoplastic and isconverted to films, sheets, wires and shaped articles by methods whichare conventional for thermoplastics, e.g., extrusion, injection moldingand thermoforming. Particular applications for the polymer productinclude containers for food and drink and parts and housings forautomotive applications.

The invention is further illustrated by the following ComparativeExamples (not of the invention) and the following IllustrativeEmbodiments which should not be regarded as limiting. The polymerproducts of the Comparative Examples and the Illustrative Embodimentswere examined by ¹³ C-NMR. All copolymer products were found to belinear alternating copolymers of carbon monoxide and ethylene and allterpolymer products were found to be linear alternating terpolymers ofcarbon monoxide and ethylene or propylene. The limiting viscositynumbers were determined in m-cresol at 60° C.

COMPARATIVE EXAMPLE I

A copolymer of carbon monoxide and ethylene was produced by charging 200ml of methanol to an autoclave of 300 ml capacity equipped with amechanical stirrer. When the contents of the autoclave were brought to85° C., an equimolar mixture of carbon monoxide and ethylene wasintroduced until a pressure of 55 bar was reached. A catalystcomposition solution was then added which comprised 6 ml methanol, 0.01mmol palladium acetate, 0.02 mmol trifluoroacetic acid and 0.01 mmol of1,3-bis(diphenylphosphino)propane. The pressure within the autoclave wasmaintained at 55 bar by continuing addition of the equimolar gaseousmixture. After 4.7 hours the polymerization was terminated by coolingthe reactor and contents to ambient temperature and releasing thepressure. The copolymer product was recovered by filtration, washed withmethanol and dried at 70° C.

The yield of copolymer was 30 g, produced at a rate of 6.0 kgcopolymer/g pd hr. The LVN of the polymer was 0.8 dl/g.

COMPARATIVE EXAMPLE II

A carbon monoxide/ethylene copolymer was produced by a proceduresubstantially similar to that of Comparative Example I except thecatalyst composition contained1,3-bis(diphenylphosphino)-2-methyl-2-diphenylphosphinomethylpropaneinstead of 1,3-bis(diphenylphosphino)propane and the reaction time was6.6 hours instead of 4.7 hours.

The yield of copolymer was 26 g produced at a rate of 3.7 kg copolymer/gPd hr. The LVN of the polymer was 0.4 dl/g.

COMPARATIVE EXAMPLE III

A terpolymer of carbon monoxide, ethylene and propylene was produced bycharging 200 ml of methanol and 24 ml of liquid propylene to anautoclave of 300 ml capacity equipped with a mechanical stirrer. Thecontents of the autoclave were warmed to 87° C. and an equimolar mixtureof carbon monoxide and ethylene was added until a pressure of 56 bar wasreached. A catalyst composition solution was then added which comprised6 ml methanol, 0.01 mmol palladium acetate, 0.2 mmol trifluoroaceticacid and 0.01 mmol 1,3-bis(diphenylphosphino)propane. The pressure wasmaintained at 56 bar by continuing addition of the equimolar mixture.After 3.7 hours the polymerization was terminated by cooling theautoclave and contents to ambient temperature and releasing thepressure. The terpolymer was recovered by filtration, washed withmethanol and dried at 70° C.

The yield of terpolymer was 21 g, produced at a rate of 5.3 gterpolymer/g Pd hr. The LVN of the terpolymer was 0.4 dl/g.

COMPARATIVE EXAMPLE IV

A terpolymer of carbon monoxide, ethylene and propylene was produced bya procedure substantially similar to that of Comparative Example IIIexcept that the catalyst composition solution contained1,3-bis(diphenylphosphino)-2-methyl-2-diphenylphosphinomethylpropaneinstead of 1,3-bis(diphenylphosphino)propane and the reaction time was6.1 hours instead of 3.7 hours.

The yield of terpolymer was 18 g produced at a rate of 2.8 kgterpolymer/g Pd hr. The LVN of the terpolymer was 0.4 dl/g.

COMPARATIVE EXAMPLE V

A copolymer of carbon monoxide and ethylene was produced by charging 200ml of methanol to an autoclave of 300 ml capacity equipped with amechanical stirrer. The contents of the autoclave were heated to 90° C.and an equimolar mixture of carbon monoxide and ethylene was added untila pressure of 55 bar was reached. A catalyst composition solution wasthen added which comprised 4.5 ml of methanol, 1.5 ml of toluene, 0.01mmol palladium acetate, 0.2 mmol trifluoroacetic acid and 0.012 mmol of1,3-bis[di(2-methoxyphenyl)phosphino]propane. The pressure in theautoclave was maintained at 55 bar by continued addition of theequimolar mixture. After 2.58 hours the polymerization was terminated bycooling the autoclave and contents to ambient temperature and releasingthe pressure. The copolymer was recovered as described above.

The yield of copolymer was 6.22 g produced at a rate of 2.3 kgcopolymer/g Pd hr. The LVN of the copolymer was 1.3 dl/g.

ILLUSTRATIVE EMBODIMENT I

A carbon monoxide/ethylene copolymer was produced by a proceduresubstantially similar to that of Comparative Example V except that thecatalyst composition comprised 6 ml of acetone, 0.01 mmol palladiumacetate, 0.2 mmol trifluoroacetate and 0.005 mmol1,8-bis[di(2-methoxyphenyl)phosphino]-2,7-bis[di(2-methoxyphenyl)phosphinomethyl]octaneand the reaction time was 1.7 hours instead of 2.8 hours.

The yield of copolymer was 8.0 g produced at a rate of 9.5 kgcopolymer/g Pd hr. The LVN of the copolymer was 1.8 dl/g.

COMPARATIVE EXAMPLE VI

A terpolymer of carbon monoxide, ethylene and propylene was produced bycharging 178 ml of methanol and 24 g of propylene to an autoclave of 300ml capacity equipped with a mechanical stirrer. The autoclave andcontents were heated to 80° C. and an equimolar mixture of carbonmonoxide and ethylene was added until a pressure of 55 bar was reached.A catalyst composition solution was then added which comprised 4.5 mlmethanol, 1.5 ml toluene, 0.01 mmol palladium acetate, 0.2 mmoltrifluoroacetic acid and 0.011 mmol1,3-bis[di(2-methoxyphenyl)phosphino]propane. The pressure within thereactor was maintained by continued addition of the equimolar mixture.After 2.45 hours the polymerization was terminated and the polymerrecovered as before.

The yield of terpolymer was 8.9 g produced at a rate of 3.4 kgterpolymer/g Pd hr. The LVN of the terpolymer was 2.1 dl/g.

ILLUSTRATIVE EMBODIMENT II

A carbon monoxide/ethylene/propylene terpolymer was produced by aprocedure substantially similar to that of Comparative Example VIIexcept that the catalyst composition solution comprised 4.5 ml methanol,1.5 ml toluene, 0.009 mmol palladium acetate, 0.2 mmol trifluoroaceticacid and 0.005 mmol of1,8-bis[di(2-methoxyphenyl)phosphino]-2,7-bis[di(2-methoxyphenyl)phosphinomethyl]octaneand the reaction time was 1.92 hours instead of 2.45 hours.

The yield of terpolymer was 20.3 g produced at a rate of 11.1 kgterpolymer/g pd hr. The LVN of the terpolymer was 2.6 dl/g.

COMPARATIVE EXAMPLE VII

A carbon monoxide/ethylene copolymer was produced by charging 1.5 literof methanol to an autoclave of 3.8 liter capacity equipped with amechanical stirrer. After the contents of the autoclave were heated to80° C., ethylene was introduced to give an ethylene partial pressure of7.6 bar and carbon dioxide was introduced to give a carbon monoxidepartial pressure of 11.4 bar. A catalyst composition solution was thenintroduced which comprised 6 ml acetone, 0.02 mmol palladium acetate,0.4 mmol trifluoroacetic acid and 0.024 mmol1,3-bis[di(2-methoxyphenyl)phosphino]-propane. The pressure in theautoclave was maintained by addition of an equimolar mixture of carbonmonoxide and ethylene. After 19 hours the polymerization was terminatedby cooling the autoclave and contents to ambient temperature andreleasing the pressure. The copolymer was recovered by filtration,washed with methanol and dried at 70° C.

The yield of copolymer was 97 g produced at a rate of 2.4 kg copolymer/gPd hr. The LVN of the copolymer was 2.1 dl/g.

ILLUSTRATIVE EMBODIMENT III

A copolymer of carbon monoxide and ethylene was produced by a proceduresubstantially similar to that of Comparative Example VII except that thecatalyst composition solution contained1,8-bis[di(2-methoxy-phenyl)phosphino]-2,7-bis[di(2-methoxyphenyl)-phosphinomethyl)-octane.instead of 1,3-bis]di(2-methoxyphenyl)phosphino]propane and the reactiontime was 17 hours instead of 19 hours.

The yield of copolymer was 90 g produced at a rate of 2.5 kg ofcopolymer/g Pd hr. The LVN of the copolymer was 2.7 dl/g.

COMPARATIVE EXAMPLE VIII

A carbon monoxide/ethylene/propylene terpolymer was produced by aprocedure substantially similar to that of Comparative Example VIIexcept that

a) quantities of ethylene, propylene and carbon monoxide were added tothe autoclave to give partial pressures of 8.5 bar, 7 bar and 23.5 barrespectively.

b) The reaction temperature was 75° C. instead of 80° C., and

c) the reaction time was 23 hours instead of 19 hours.

The yield of terpolymer was 170 g produced at a rate of 3.5 kg ofterpolymer/g Pd hr. The LVN of the terpolymer was 1.9 dl/g.

ILLUSTRATIVE EMBODIMENT IV

A carbon monoxide/ethylene/propylene terpolymer was produced by aprocedure substantially similar to that of Comparative Example VIIexcept that the catalyst composition solution contained 0.012 mmol of1,8-bis[di(2-methoxyphenyl)phosphino]2,7-bis[di(2-methoxyphenyl)phosphinomethyl]octaneand the reaction time was 4.5 hours instead of 23 hours.

The yield of terpolymer was 40 g produced at a rate of 4.2 kgterpolymer/g Pd hr. The LVN of the terpolymer was 3.1 dl/g.

What is claimed is:
 1. An aromatic tetradentate phosphine of the formula##STR3## wherein R independently is an alkoxy-substituted aryl group ofup to 10 carbon atoms, wherein at least one alkoxy substituent islocated in a ring position ortho to the carbon atom through which thearyl group is connected to a phosphorus atom, and n is an integer from 0to about
 14. 2. The phosphine of claim 1 wherein n is an integer from 0to about
 10. 3. The phosphine of claim 2 wherein R is selected from thegroup consisting of 2-methoxyphenyl, 2-ethoxyphenyl,2,4-dimethoxyphenyl, 2,6-diethoxyphenyl, and 2,4,6-trimethoxyphenyl. 4.The phosphine of claim 2 wherein R is 2-methoxyphenyl.
 5. The phosphineof claim 2 of the formula1,8-bis[di(2-methoxyphenyl)phosphino]-2,7-bis[di(2-methoxyphenyl)phosphino-methyl]octane.